The Effect of Similarity: Non-Spatial Features Modulate Obstacle Avoidance

Abstract

The introduction of non-target objects into a workspace leads to temporal and spatial adjustments of reaching trajectories towards a target. If the non-target is obstructing the path of the hand towards the target, the reach is adjusted such that collision with the non-target, or obstacle, is avoided. Little is known about the influence of features which are irrelevant for the execution of the movement on avoidance movements, like color similarity between target and non-target objects. In eye movement studies the similarity of non-targets has been revealed to influence oculomotor competition. Because of the tight neural and behavioral coupling between the gaze and reaching system, our aim was to determine the contribution of similarity between target and non-target to avoidance movements. We performed 2 experiments in which participants had to reach to grasp a target object while a non-target was present in the workspace. These non-targets could be either similar or dissimilar in color to the target. The results indicate that the non-spatial feature similarity can further modify the avoidance response and therefore further modify the spatial path of the reach. Indeed, we find that dissimilar pairs have a stronger effect on reaching-to-grasp movements than similar pairs. This effect was most pronounced when the non-target was on the outside of the reaching hand, where it served as more of an obstacle to the trailing arm. We propose that the increased capture of attention by the dissimilar obstacle is responsible for the more robust avoidance response.

Reaching around obstacles accounts for uncertainty in coordinate transformations

“…That is, as all participants performed their movements with their right hand, passing obstacles from the left side requires higher curvature to avoid any possible collision with the performing arm (as opposed to only considering the fingertips or hand). This is in accordance with what has been reported in many previous studies (Chapman & Goodale, 2008;De Haan et al, 2014;Menger et al, 2013;Menger et al, 2012;Ross et al, 2018;Ross et al, 2015;Voudouris et al, 2012). Hence, together with previous findings, our results suggest that humans are trading of between minimizing the likelihood of obstacle collision (by increasing the curvature) and minimizing the biomechanical costs (by decreasing the curvature).…”

“…However, one needs to consider that the shift caused by removing the visual feedback for leftward movements while the head was straight was already stronger than for the rightward movements (Figure 7B; see the difference between the black solid line -without visual feedback and the black dotted line -with visual feedback. This observation is in line with previous studies (Chapman & Goodale, 2008;De Haan et al, 2014;Menger, Dijkerman, et al, 2013;Menger et al, 2012;Ross et al, 2018;Ross et al, 2015), and as Menger et al (2013) illustrated, this is mainly due to the degree of obstructiveness of the obstacle. This indicates that people adapt their compensatory behavior if it is necessary.…”

The Effect of Gaze Position on Reaching Movements in an Obstacle Avoidance Task

“…The asymmetry between left and right obstacle fixation may be due to the fact that all of our participants reached with their right arm. Therefore the right obstacle was more obstructive for the movement, as it was placed on the same side as the forward-reaching arm (for similar findings see [ 30 , 35 , 37 , 38 , 44 ]). The closer the obstruction is to the movement path, the more relevant it becomes for movement planning.…”

It is the flash which appears, the movement will follow: Investigating the relation between spatial attention and obstacle avoidance

“…Given that obstacles are represented in the attentional landscape, it remains to be seen what the exclusive contribution of attention itself is to the avoidance response. In earlier experiments, attentional manipulations had co-occurred with changing features of the obstacle (e.g., its color similarity to the target; Menger, Dijkerman, & Van der Stigchel, 2013 ), or feature manipulations of the obstacle co-occurred with attentional changes. Now, for the first time, the present experiments offer the opportunity to study the effect of attention without changing the spatial features of the to-be-avoided obstacles.…”